This invention relates to the control of electric water heaters and, in particular, to the control of dual heating elements often found in such water heaters.
Electric water heaters often have both an upper heating element and a lower heating element extending into a tank containing the water that is to be heated. The upper heating element heats water in the upper portion of the tank whereas the lower heating element heats water in the lower portion of the tank. The heating of the water by each heating element is premised on there being sufficient water in the tank to submerse both heating elements. There may, however, be one or more situations where the upper heating element is not immersed in water. One such situation can occur when the tank is being initially filled with water. The air in the tank will be compressed as the tank is initially filled with water. The compressed air may lead to a premature cut-off of the water feed to the tank before the water level rises above the upper heating element.
A subsequent demand to heat the water in the tank will normally lead to activation of the upper heating element. The thus activated heating element will remain on until a sensor associated with the heating element reaches set point temperature. This may lead to a premature burning out of the upper heating element since it will most likely remain on for an extended period of time in an attempt to heat the air surrounding the sensor to the set point temperature.